1. Field of the Invention
The present invention generally relates to rock reinforcement methods and systems used in the mining and civil engineering industry where openings in rock, whether blasted or excavated, are reinforced to preserve the opening size and prevent collapse and, more particularly, is concerned with an improved reinforcement system having apparatus and method for reinforcing the rock mass around the opening regardless of the orientation of joints or fractures in the rock mass. The improved rock reinforcement system enhances stability and strength of the opening.
2. Description of the Prior Art
Rock reinforcement methods and procedure, evolve around three fundamental elements and their combinations, namely rock bolts of different designs and forms, use of cables and prestressed cables, and utilization of concrete in form of grouting or shotcrete applications. Rock bolts are most useful in bedded rock formation, where purpose of bolting is to tighten together several layers to combine their ability to resist a bending moment. Typically, in the Western United States rock bolts such as those manufactured by CF&I Steel Corporation with expansions shells manufactured by Pattin Mfg. Co. are used in these applications. However, rock bolts utilization has problems which are as basic as bolt spacing. In actual practice, with no clear knowledge of bedding, rock mass fracture, and jointed in all directions, the questions of bolt length, bolt diameter and spacing are quite different and sometimes outright impossible to answer. Rock bolt reinforcement design has disadvantages in rock mass formations having vertical joints perpendicular to cross section of the opening. In such cases some rock layers will be out of the influence of the bolting and will become loose and present a hazardous situation. Solutions for these situations include the use of a wire mesh held up by the rock bolt plates or possibly in combination with shotcrete to function as passive support. The combination of rock bolt lateral tension in the vertical direction and the horizontal tensioning of the wire mesh and shotcrete provides the desired reinforcement of the opening. Other solutions to the problem could involve the construction of a back reinforcement utilizing the principles of the Roman arches. Such solutions known to the mining industry are rock reinforcement methods involving rebar with rock stabilizers, Birminham Bolt Company rod trusses and Scott's cable sling. Although these method and associated system apparatus provide an adequate solution they are limited in providing a continuous reinforcement solution to the problem in that effective back reinforcment can only be achieved in a small area, i.e. to that rock mass between two rock bolts and not throughout an entire excavation or drift drill hole pattern.
Consequently, a need exists for a rock reinforcement system and method having apparatus which will overcome the limitation of not providing a continuous and hazard free reinforcement while effectively solving the problem of providing a two directional reinforcement of the back or roof of a mine drift or similar excavation regardless of the orientation of the joints or fractures in the rock mass.